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From Colm O hEigeartaigh <cohei...@apache.org>
Subject Re: Anonymous PKINIT signatures
Date Wed, 27 Jul 2016 12:58:59 GMT
Hi Jiajia,

It's the client that's anonymous here, and not the KDC. This page leads me
to believe that the KDC does in fact sign the response to the client:

http://web.mit.edu/kerberos/krb5-devel/doc/admin/pkinit.html

" For anonymous PKINIT, a KDC certificate is required, but client
certificates are not.".
"The result of this operation will be in two files, kdckey.pem and kdc.pem.
Both files must be placed in the KDC’s filesystem. kdckey.pem, which
contains the KDC’s private key, must be carefully protected."

Colm.

On Tue, Jul 26, 2016 at 3:08 AM, Li, Jiajia <jiajia.li@intel.com> wrote:

> Hi Colm,
> >> However, the client doesn't use the certificate to verify a signature,
> and thus proving that the KDC knows the private key associated with the
> cert. Is this correct?
> You are right. I think anonymous case, not actually signed.
> Thanks,
> Jiajia
>
>
> From: Colm O hEigeartaigh [mailto:coheigea@apache.org]
> Sent: Friday, July 22, 2016 11:22 PM
> To: Li, Jiajia <jiajia.li@intel.com>
> Cc: kerby@directory.apache.org
> Subject: Re: Anonymous PKINIT signatures
>
> Hi Jiajia,
> So if I understand you correctly, what you are saying is that it is
> sufficient to verify that the Subject (alternative name) of the Certificate
> matches that of the "known principal" of the KDC? In other words, the KDC
> is not doing any asymmetric signature, it is just "presenting" the
> certificate to the client. The client verifies that the certificate is
> trusted, and then verifies that the KDC principal matches the certificate.
> However, the client doesn't use the certificate to verify a signature, and
> thus proving that the KDC knows the private key associated with the cert.
> Is this correct?
> It's a bit unusual from a security POV but I think it's ok. We're
> verifying trust in the certificate path and we're putting a hard constraint
> on the Subject of the certificate. A malicious KDC/MITM could forge a
> certificate, but then trust validation would fail, or else get a
> certificate for another KDC, but then the constraint would fail. So I think
> it's ok.
>
> Colm.
>
> On Fri, Jul 22, 2016 at 3:40 AM, Li, Jiajia <jiajia.li@intel.com<mailto:
> jiajia.li@intel.com>> wrote:
> Hi Colm,
> >> >However, I can't see where it is signing the response with the private
> key associated with the KDC. This is a requirement for anonymous PKINIT
>
> Yes, you are right. The  "Identity" should be used in anonymous PKINIT.
> But now in client PkinitPreauth, start from line 393, we skip to use the
> certificateSet which is returned by server, so now the code can't verify
> the kdc sans, edu and so on. Such as the function
> cryptoRetrieveX509Sans#PkinitCrypto is marked as TODO.
>
>
> Thanks
> Jiajia
>
>
> -----Original Message-----
> From: Colm O hEigeartaigh [mailto:coheigea@apache.org<mailto:
> coheigea@apache.org>]
> Sent: Thursday, July 21, 2016 7:27 PM
> To: kerby@directory.apache.org<mailto:kerby@directory.apache.org>
> Subject: Anonymous PKINIT signatures
>
> Hi all,
>
> I'm continuing to look at anonymous PKINIT as implemented in Kerby. I'm a
> bit puzzled by a few things relating to signatures and would welcome some
> feedback.
>
> Looking at the server PkinitPreauth, it appears that Diffie-Hellman is
> used to establish a shared secret key with the client. However, I can't see
> where it is signing the response with the private key associated with the
> KDC. This is a requirement for anonymous PKINIT, unless I am mistaken?
>
> Similarly, on the client side, it's not enough just to verify trust in the
> Certificate that's presented, it also needs to be using the Certificate to
> verify some signed data, to make sure that the KDC knows the private key
> associated with the Certificate...
>
> I've updated the code so that the server at least includes the "Identity"
> Certificate in the response to the client.
>
> Thanks,
>
> Colm.
>
>
> --
> Colm O hEigeartaigh
>
> Talend Community Coder
> http://coders.talend.com
>
>
>
> --
> Colm O hEigeartaigh
>
> Talend Community Coder
> http://coders.talend.com
>



-- 
Colm O hEigeartaigh

Talend Community Coder
http://coders.talend.com

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